The singer called out the president for playing his upbeat song hours after "the mass murder of 11 human beings" at a synagogue.

Pharrell Williams has sent Donald Trump a legal challenge over his use of the song Happy on the day of the Pittsburgh synagogue massacre.

Lawyers for the singer issued Mr Trump a cease and desist letter after he played the song at a political event in Indiana "on the day of the mass murder of 11 human bring at the hands of a deranged 'nationalist'".

The president had played the song at the Future Farmers of America rally in Indiana just hours after the mass shooting killed 11 people - predominantly elderly Jewish Americans from a tight-knit community - as they worshipped on Saturday morning.

During his speech to the Future Farmers of America, Trump entered to the song “Happy;” joked about cancelling tonight’s rally because he‘s having a bad hair day; and used the anti-Semitic "globalist" dogwhistle hours after a mass shooting at a synagogue.pic.twitter.com/u8ANgnWzzE